1. Field of the Invention
This invention relates to an optical disc apparatus, and more particularly relates to an optical disc apparatus which is suitably applied to a magneto-optic disc apparatus. In the present invention, by correcting the signal level of the first and second light quantity detection signal for generating a reproduction signal from a differential output based on the signal level of a wobble signal component detected from the reproduction signal and the phase detection result or by extracting and subtracting a wobble signal component in the respective first and second light quantity detection signals, leakage of a wobble signal to a reproduction signal is reduced.
2. Description of Related Art
Heretofore, in a mini-disc apparatus, a laser beam is irradiated on a mini-disc with reference to grooves formed on the mini-disc having the optical disc structure to get an access to the mini-disc.
In detail, in manufacturing process of mini-discs, a carrier signal having a predetermined frequency is frequency-modulated by use of address information of each recording/reproduction position to generate a wobble signal. Grooves which carries guide grooves for a laser beam are formed on the information recording side, when the grooves are formed in waving form by the wobble signal.
The mini-disc apparatus reproduces a wobble signal having the signal level, which varies correspondingly to the waving of the groove, from a return beam obtained by irradiating a laser beam onto a mini-disc to acquire the address information of the laser beam irradiation position from the wobble signal. The mini-disc apparatus takes an access to a mini-disc with reference to the address information.
In the access to a mini-disc, a mini-disc apparatus detects a reproduction signal having the signal level which varies correspondingly to the change of the polarization plane of the return beam to obtain a reproduction signal having the signal level which varies correspondingly to a mark and space which are recorded on a mini-disc by applying electro-optical Kerr effect, and the reproduction signal is processed to reproduce a thermomagnetically recorded data.
In the operation of a mini-disc apparatus, a wobble signal can leak into a reproduction signal. If the leakage of wobble signal can be reduced, then the waveform deterioration of reproduction signal will be suppressed and the error rate will be improved.
As the result of detailed examination of the leakage, it was found that the leakage depends on the in-plane birefringence of a mini-disc substrate which a laser beam passes through, and the birefringence depends on the radial direction of the mini-disc. Further, the leakage depends on the magnitude of birefringence and also depends on the birefringent azimuth as shown in FIG. 5. In FIG. 5, the axis of ordinate represents the ratio of the wobble signal corresponding to the reproduction and the axis of abscissa represents the azimuth of birefringence, for the case that of the magnitude of birefringence is 60 nm for two ways of a laser beam.